I bet Umbro has a very big say in what the team wears: and they want to show off the new(ish) away kit. So long as they don't clash with the opponents colour system, it doesn't matter which one they wear.
It depends on the opposite team. At home they play in white, and away it's red unless they are playing against a team who's home kit is red. Then they play in white. I will probably be proved wrong but that is what I have always thought
I think whoever is the designated 'home' team, in this case England, gets to choose which kit they where. Presumably they chose the red away kit as it was brand new and likely wanted to show it off.
Did something similar not happen in the last World Cup when England played Argentina? We were the 'home' team, and we chose to wear the red kit as we wore red when we last beat them in a World Cup?
Please feel free to correct me, as this is all just a vague memory of stuff I've heard in the past!